Incident Mycobacterium tuberculosis infection in household contacts of infectious tuberculosis patients in Brazil

Edward C Jones-López,Mary Gaeddert,Moises Palaci,Patricia Marques-Rodrigues,Solange Vinhas,Jerrold J Ellner,Padmini Salgame,Lucilia Pereira Dutra-Molina,Rodrigo Ribeiro-Rodrigues,Avery I Mcintosh,Reynaldo Dietze,Laura F White,Carlos Acuña-Villaorduña,David Alland,David Jamil Hadad,Geisa Fregona

doi:10.1186/s12879-017-2675-3

Abstract

BackgroundIn household contact investigations of tuberculosis (TB), a second tuberculin skin test (TST) obtained several weeks after a first negative result consistently identifies individuals that undergo TST conversion. It remains unclear whether this delay in M. tuberculosis infection is related to differences in the infectious exposure, TST boosting, partial host resistance, or some other factor.MethodsWe conducted a household contact study Vitória, Brazil. Between 2008 and 2013, we identified culture-positive pulmonary TB patients and evaluated their household contacts with both a TST and interferon gamma release assay (IGRA), and identified TST converters at 8–12 weeks post study enrollment. Contacts were classified as TST-positive (≥10 mm) at baseline, TST converters, or persistently TST-negative. We compared TST converters to TST-positive and to TST-negative contacts separately, using generalized estimating equations.ResultsWe enrolled 160 index patients and 838 contacts; 523 (62.4%) were TST+, 62 (7.4%) TST converters, and 253 (30.2%) TST−. TST converters were frequently IGRA− at 8–12 weeks. In adjusted analyses, characteristics distinguishing TST converters from TST+ contacts (no contact with another TB patient and residence ownership) were different than those differentiating them from TST− contacts (stronger cough in index patient and contact BCG scar).ConclusionsThe individual risk and timing of M. tuberculosis infection within households is variable and dependent on index patient, contact and environmental factors within the household, and the surrounding community. Our findings suggest a threshold effect in the risk of infection in humans.

Highlights

In household contact investigations of tuberculosis (TB), a second tuberculin skin test (TST) obtained several weeks after a first negative result consistently identifies individuals that undergo TST conversion
TST and interferon gamma release assay (IGRA) testing and retesting protocol We evaluated contacts for M. tuberculosis infection with both TST and IGRA (Quantiferon Gold-In-Tube, Quiagen, U.S.A.), as described [22]
Comparison of TST converters vs. persistently TSTnegative contacts In an unadjusted analysis that compared TST converters vs. TST-negative contacts (Table 1 and Additional file 1: Table S1), TST converters were more likely to have an index TB patient with more severe cough as measured by higher visual analog cough scale (VACS) scores or lower Leicester Cough Questionnaire (LCQ) scores, to sleep in the same room as the index patient, and to have ≥6 h/day of contact with the index patient

Summary

Introduction

In household contact investigations of tuberculosis (TB), a second tuberculin skin test (TST) obtained several weeks after a first negative result consistently identifies individuals that undergo TST conversion. It remains unclear whether this delay in M. tuberculosis infection is related to differences in the infectious exposure, TST boosting, partial host resistance, or some other factor. A third group of contacts can only be identified when placing a second test, usually weeks after the initial test is negative, to identify individuals that undergo TST or IGRA conversion [11, 13]

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